A liquid crystal polyester resin (LCP) capable of forming an anisotropic melt phase is a thermoplastic resin having many desirable characteristics such as high strength, high rigidity, high thermal resistance, and easy moldability, but there are also commercial disadvantages such that the mold shrinkage and mechanical properties tend to vary depending upon the molecular chain orientation and the direction in which the measurement is conducted, and the purchase price tends to be high.
On one hand, a polyester resin such as a polycarbonate resin (PC), etc. that does not form an anisotropic melt phase is relatively cheap, but the physical properties thereof such as rigidity are inferior to that of a liquid crystal polyester. More specifically, the rigidity is insufficient for use in the formation of a thin housing, so that thickening is necessary when designing a part constructed therefrom. There are thus some limitations for applications intended to carry out the miniaturizing and weight-reducing trends that are operative in the electric, electronic, and communication equipment fields.
Thus, in order to make a good use of the advantageous properties of the LCP and the polyester resin not forming an anisotropic melt phase, it has been tried to mix them in an effort to compensate for the disadvantages of each. However, in an injection molded product made from a resin composition wherein a small quantity of an LCP is blended with a polyester resin that does not form an anisotropic melt phase, the characteristics of LCP, such as high strength, high rigidity, high thermal resistance and easy moldability are not put to a good use and the mechanical strength of the resulting blend decreases markedly. The cause thereof is that the high mechanical properties of LCP are only produced when there is molecular orientation created by shear stress and tensile stress during molding. That is, in a resin composition obtained by only blending a polyester resin not forming an anisotropic melt phase and a small quantity of LCP, although molecules are orientated in areas near the surface layer of the product, areas other than the surface layer have a morphology wherein the polyester resin that does not form an anisotropic melt phase serves as a matrix and almost all LCP is dispersed somewhat spherically without any reinforcing effect. Only after the LCP is fibrillated within a product during molding, is the LCP molecularly orientated in the direction of the product length in a fibrous configuration having a reinforcing effect.
On the other hand, if the proportion of LCP is increased and the polyester resin not forming an anisotropic melt phase is decreased, there is produced a morphology wherein the LCP is a matrix and the PC is dispersed as islands therein. As a result, the advantageous properties of the polyester resin not forming an anisotropic melt phase cannot be put to good use and its usefulness in the blend is lessened.
Thus, there have been considered some methods by which a thermoplastic resin, such as LCP and PC, are extruded with drawing at a temperature that melts both resins, to form a molding composition wherein the LCP is present in a fibrous form having a large aspect ratio. The resulting molding composition is then molded at a temperature at which LCP is not molten and only the other thermoplastic resin, such as the PC, is molten, to form a molded product containing fibrous LCP which exhibits a reinforcing effect, as described in the Specifications of Japanese Patent Open-laid Application Nos. Hei 5-70700 and Hei 5-112709.
However, the LCP should be kept in its orientated state in fibrous form by preliminarily extruding and drawing the same, or alternatively, the resin composition should be subjected to high shear conditions when placed in the mold that are designed to fibrillate the LCP.
In the former case, the flowability is poor and the possibility for molding is limited. In the latter case, the appearance of the product may suffer and also insufficient strength may result because of insufficient fibrillation.